Cannons made in Pittsburgh gave Union an edge

Thomas Jackson Rodman never led troops into battle, but his groundbreaking experiments with cannons and gunpowder gave his fellow Union soldiers a valuable advantage.

As a cadet at the U.S. Military Academy in West Point, N.Y., the Indiana native excelled at math and metallurgy. He loved to watch the casting of iron cannons at nearby West Point Foundry. After graduating in 1841, he was assigned to the Allegheny Arsenal in Pittsburgh. For the next two decades, his experiments made him a major pioneer in the field of metallurgy.

Rodman's method of casting a hollow cannon gave the Union Army a strategic advantage, said Les Jensen, curator of arms and armor at West Point Museum in West Point, N.Y. Cast iron is brittle, Mr. Jensen said, and during the 1800s, some cannons either exploded during testing or later on the battlefield. Cannons could weigh as much as 300 pounds.

To cast a cannon in a foundry, a big pit was dug and the weapon was made in one piece from a mold. Later, technicians drilled out a long tube, called a bore, through which a cannon ball was fired. During casting, as hot iron cooled from the outside to the inside, internal stresses were created in the metal, which weakened it. Some foundries tried, without much success, to reinforce cannons with wrought iron at their rear or breach.

"That's where the greatest amount of strain is because when the powder goes off and you have to push that projectile down the gun, you are putting a lot of strain on the rear end of that gun," Mr. Jensen said.

Rodman's mold included a hollow bore that allowed for cool water to circulate through it continuously during production. This made the metal much more cohesive, Mr. Jensen said.

During the Civil War, artillery soldiers used a long spike to push a big bag of gunpowder down the bore, then inserted a cannon ball. Through a touch hole, they tore the powder bag and inserted a friction primer, a little tube with a wire attached to it. Yanking on that wire shot fire into the gun and set off the powder charge.

The first hollow-bore guns were cast here in 1845, and Rodman received a patent two years later. He often shuttled between the Allegheny Arsenal in Lawrenceville and the Fort Pitt Foundry, which was in the 1200 block of Smallman Street in the Strip District, just across the street from what is now the Senator John Heinz History Center.

The U.S. government did not start to use Rodman's cannons until the late 1850s. After the Civil War broke out in 1861, Rodman's cannons were effective in deterring Confederate forces from attacking Union forts at harbors along the Eastern seaboard.

Michael Kraus, curator of Soldiers and Sailors Memorial in Oakland, said Rodman's innovations led to greater advances in metallurgy.

"He invented a way to pour large quantities of iron and have them cool evenly. That just opened the door for steel. It was like jumping into a new age."